This invention relates to a process for the recovery of nickel and/or cobalt from a concentrate.
Nickel sulphide ores are presently treated in commercial practise by a variety of processes in which the first step is almost always a physical concentration by flotation to upgrade the Ni content, typically, from a range of 0.5% to 2.0% up to 7 to 25% Ni, as a concentrate. The subsequent treatment of this concentrate is usually pyrometallurgical (smelting) to produce a Ni matte or an artificial high grade sulphide with about 20% to 75% Ni.
The matte is then generally refined to nickel products by hydrometallurgical techniques.
This combination of pyrometallurgical/hydrometallurgical processing of Ni concentrates is now well established commercially with a number of variations, particularly in the hydrometallurgical portion. Most processes recover some portion of the associated metal values where present, such as copper and cobalt. In addition, a leach residue containing precious metals, such as gold and silver, as well as platinum group elements, e.g. platinum and palladium, is often produced for subsequent recovery of contained values.
This treatment scheme has some inherent drawbacks. Those associated with the pyrometallurgical step, include:
(i) Production of smelter gases including SO2, which must now be treated in an acid plant to produce sulphuric acid byproduct, which frequently is difficult to market from a remote location. (The capital and operating costs of such acid plants impact on the overall economies of the process.)
(ii) Losses of nickel and particularly cobalt into the slag produced during smelting, often more than 50% of cobalt input.
(iii) High costs of smelting in general, particularly for low grade concentrates ( less than 10% Ni).
(iv) Difficulty in treating certain concentrates with deleterious elements, such as magnesium (Mg) and arsenic (As).
The hydrometallurgical steps for treating Ni matte vary considerably but all known commercial processes have one or more of the following disadvantages:
(i) High costs for reagents such as caustic soda or ammonia, required for neutralization.
(ii) Large byproduct production, such as ammonium sulphate or sodium sulphate, which are difficult to market.
(iii) High energy costs, due to large temperature changes during the process.
(iv) Complex and costly process flowsheet, leading to high capital and operating costs.
As an alternative to the established pyrometallurgical/hydrometallurgical route outlined above, there is one known process using wholly hydrometallurgical steps, that treats concentrates without smelting. It uses a pressure leaching technique with ammoniacal solution. This avoids most of the disadvantages associated with the smelting processes, but unfortunately still suffers from all of the listed disadvantages of the known hydrometallurgical routes, and in fact is not even as efficient overall as the best of the pyrometallurgical/hydrometallurgical routes.
Copper or nickel sulphide ores often also contain other metal values, such as cobalt, as well as precious metals, such as gold and silver and the platinum group metals. Since these ores are typically low grade ores, in so far as copper/nickel is concerned, and also have a high sulphur to copper/nickel ratio, the economical extraction of copper, nickel and cobalt values have been problematical. Some sulphide ores contain such low copper/nickel values that the recovery of precious metals must be high in order to render the process economical. Due to the pyrite content of some ores, the recovery of gold by conventional cyanidation is often difficult, which also renders the treatment of the ore uneconomical.
According to the invention there is provided a process for the recovery of nickel and/or cobalt values from a concentrate containing nickel and/or cobalt hydroxide, comprising the steps of subjecting the concentrate to a leaching stage with an ammonium solution to produce a leach solution containing nickel and/or cobalt values and a residue; and controlling the concentration of nickel in the leach solution to a maximum value of about 3 to 25 g/l. preferably 8 to 15 g/l and more preferably 10 g/l.
The term xe2x80x9cconcentratexe2x80x9d in this specification refers to any material in which the metal value content has been increased to a higher percentage by weight as compared with the naturally occurring ore and includes man made artificial sulphide ore, such as matte, and metal values precipitated as solids such as hydroxides and sulphides.
Further objects and advantages of the invention will become apparent from the description of preferred embodiments of the invention below.